ÆChoosing between encoding speed and quality
‐Many codecs offer a control that specifies a trade‐off between encoding time and quality. The faster modes typically perform much less exhaustive motion estimation. ‐ Generally, big speed changes cause much smaller quality gains
‐The correct trade‐off between speed and quality varies depending on the project. ‐ For DVD projects, titles under an hour won’t gain much by slower, higher‐quality encoding because the data rate is so high. Web‐distributed content almost always benefits from the slower, high‐quality encoded files, because bandwidth is so often the limiting factor for web video.
ÆSetting frame size
Frame size (also called resolution) is the height and width of the final video frame, measured in pixels. The data rate changes in proportion to the area of the frame (height x width).
‐Thus, converting from 320 x 240 to 640 x 480 would require about four times the data rate, but converting to 192 x 144, you could reduce the data rate down to one‐third. Because there are fewer pixels, pixel quality becomes more important.
‐Most codecs and formats require the height and width of a video to be divisible by two and give best compression efficiency when height and width are divisible by 16.
ÆSpecifying aspect ratio
‐An important facet of frame size is aspect ratio. Most web and CD‐ROM formats use square pixels, and many formats only support square pixels.
‐Conversely, the disc‐based VCD, SVCD, and DVD formats only use nonsquare pixels. ‐ It’s important to figure out the target aspect ratio first, and then make sure that the frame size you choose gives the correct aspect ratio given the picture shape in which the content is delivered.
Adjusting the frame rate
Higher frame rates appear smoother, and lower frame rates appear choppier.
ÆAnything below 20 fps doesn’t appear smooth, and below 10 fps, the video looks more like a filmstrip than moving video.
ÆReducing or increasing the frame rate has much less effect than frame size on the data rate because reducing the frame rate requires encoding twice as much motion for each frame, a process that requires more bits for each frame. Also, each frame appears for twice as long, so there’s more
